ORIGIN OF THE CEREBRAL NERVES. 509 



of the accessory nerve below the decussation of the pyramids 

 lie in a plexiform breaking up of the anterior cornu external 

 to the processus lateralis (formatio reticularis), and the roots, 

 which in the upper part were seen to diverge from each other 

 anteriorly, and then traverse the lateral cord transversely (fig. 

 258, xi ; 261, xi), now run in close proximity and parallel to 

 the posterior cornua, without, however, passing through their 

 gelatinous substance. The latter deviation is the rule for the 

 whole accessory tract (Stilling) (fig. 258, xi). 



The nuclei of the hypoglossal nerves lie near the middle line 

 of the grey floor, where the groove of the calamus scriptorius is 

 open on the inner side, but where the central canal is closed in, 

 in front of the vago-accessory nuclei, and in the tracts of origin 

 of the roots of the hypoglossal nerves. On each side an in- 

 ternal and an external nucleus are to be distinguished, lying 

 close to one another (tig. 258, XII 1 , xn 2 ), which are separated 

 from the small clusters of nerve corpuscles of the anterior 

 nucleus situated in the root itself, by their connections pro- 

 ceeding from the raphe. The large cells of the hypoglossal 

 nuclei, which are anteriorly scattered for a long distance into 

 the raphe, are 60 JJL in length, and 21 /j. thick, and are adherent 

 by their long axes to the convoluted arcuate fasciculi in the 

 interior of the posterior nucleus I have now to describe. 



I will, however, first refer to a connection which occurs be- 

 tween the hypoglossal nuclei and the posterior (reflex) division 

 of the medulla oblongata, which is traversed by the origin of 

 the posterior column and other forms of fibrae arcuatse. 



Immediately external to the root of the hypoglossal nerve we 

 observe fine grey radiating nervous fasciculi distinctly proceeding 

 from the nuclei of origin of the hypoglossus, which reach large 

 cells parallel to them, lying about twenty-five millimeters in 

 front of the hypoglossal nucleus, and by means of their processes 

 form an apparent connection with fibrse transversse. These ra- 

 diating fibres essentially contribute to produce the fine areation 

 in the transverse section of the projection system, by decussating 

 with the transverse fasciculi, but must, however, be clearly 

 distinguished from the similar boundaries of the fine areas pro- 

 duced by anastomoses of the transverse fasciculi (fig. 258, be- 

 tween XI and xn). These fasciculi, like the six roots mentioned 



